In a significant precedent for Google and other companies developing autonomous car technology, the National Highway Transportation Safety Administration (NHTSA) has ruled that the software behind some automated cars should be considered the driver.

The decision was contained in a letter that was sent from the federal agency to Google, now a unit within a wider company named Alphabet.

For automakers, the agency’s ruling is a key step in being able to mass-produce self-driving vehicles and sell them to consumers. And on a philosophical level, it’s the most high-profile instance in which a federal agency has said a computer fits the legal definition of a human.

The lengthy document was in response to a request submitted in a November by Google to see how federal safety regulations – such as rules about seats, mirrors and brake pedals – would apply to a self-driving car. The government agency sets and enforces safety standards for US vehicles.

Google wanted to know, for example, if its autonomous vehicles had to abide by a rule that requires vehicles to have an “occupant seat for the driver”.

The government agency responded that, because it interprets the term “driver” as the self-driving system, “the ‘driver’ in this provision would not need an occupant seat”.

Google’s cars “will not have a ‘driver’ in the traditional sense that vehicles have had drivers during the last more than one hundred years,” the NHTSA wrote in the letter, which was sent last week and unearthed by Reuters on Tuesday. “If no human occupant of the vehicle can actually drive the vehicle, it is more reasonable to identify the ‘driver’ as whatever (as opposed to whoever) is doing the driving.”

Tech firms and automakers have been experimenting with self-driving cars for years. They can often be seen on the roads around Google’s Silicon Valley campus – though usually with a human ready to take the controls if needed.

But these vehicles have operated in a patchwork of state, local and federal regulations. If any automaker wanted to mass produce a driverless car to sell to consumers, it would need approval from the NHTSA.

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Google in many ways has led a race among tech firms and automakers to bring driverless cars to the masses. Other competitors include Tesla, General Motors and Toyota. Uber, the ride-hailing app, has a research facility in Pittsburgh, Pennsylvania, working on technology that could replace its fleet of human drivers.

Google says its cars have self-driven more than 1m test miles, with trips in California, Texas and Washington state. Its latest model lacks a steering wheel and a brake lever.

That’s for safety reasons, according to the NHTSA letter. The tech company told regulators these features are missing because they “could be detrimental to safety because the human occupants could attempt to override” the self-driving system’s decisions, according to the letter.

The agency’s ruling likely won’t have any immediate effect on Google’s operations.

Although the NHTSA said it agreed the software was the driver in a Google car, it also said it had no test to evaluate whether the software was a good one. It also said the company would have to work around federal rules requiring cars to have basic safety features – like brake pedals. This could be done by having rules changed or by Google petitioning for an exemption, the agency said.

“Those standards were drafted at a time when it was reasonable to assume that all motor vehicles would have a steering wheel, accelerator pedal, and brake pedal, almost always located at the front left seating position, and that all vehicles would be operated by a human driver,” the government said.

The US Department of Transportation so far has supported Silicon Valley’s push to take humans out of the driver’s seat, viewing it as a way to minimize traffic deaths. The White House budget, released this week, includes $4bn over the next decade to promote the development of self-driving cars.